This converter reads the channels with the Web Audio API and writes an uncompressed 16-bit mono WAV. Mix mode averages the channels sample by sample, while left-only and right-only modes help when an interview, camera, or field recorder captured the useful microphone on just one side.
A mono file can be simpler for speech, phone playback, accessibility mixes, and editors that require a one-channel source. Browser codec support varies, so MP3 and WAV are the safest inputs; M4A, OGG, FLAC, and other audio formats work where your browser can decode them.